It's when you suddenly switch from idealization to devaluation of usually another person, sometimes yourself, sometimes the world or society or a group. Like if I'm absolutely in love with a person and they said they'd call at 3pm and it's 3:06 and they acted distracted last I talked to them, that'll trigger my "core content" (the childhood wounds and resulting fear of abandonment/lack of sense of self/etc.) and, I think out of fear and wanting to protect myself, I'll hate them with such intensity and that'll usually trigger rage.

There are some good sources on Youtube (Daniel Fox I think his name is--he has a workbook too). He's an expert in personality disorders and is really non-judgmental. I do remember thinking that in his videos he implies "will" rather than "can," but if you take what's relevant and leave what isn't that's the way to go. BPD is so wildly varying person to person, and there are other disorders it can be confused with and a lot of people are misdiagnosed as a result. Both add to why there's not a lot of good, accurate information out there--because there's no real consistent information to be found.

Dr. Fox proposes there are four types of BPD, and that some people have it purely genetically and some purely environmentally but a majority a mixture of some sort. We'll pretend he's right here. Who's to say someone with mostly genetically impulsive BPD will benefit from the same treatment as the one with mostly environmentally discouraged BPD or even mostly environmentally impulsive BPD? Just because they have the same name, doesn't mean they'll be successfully treated the same. Some people with MDD do great on Prozac, some people don't do well on any antidepressant at any dose but certain therapies or another class of med has helped. Idk why BPD would be much different